Vein patterns inside a person's fingers may be used to verify a person's identity. Vein patterns are different for each finger and for each person. Because they are hidden underneath the skin's surface, forgery is extremely difficult. Also, they are not changed by aging, unlike other major biometrics such as fingerprint, face and voice.
Sony Corp. and Hitachi Ltd. have each developed finger vein authentication apparatus that use two-dimensional (2D) projection images of vein patterns. These apparatus use multiple near infrared LED (light emitting diodes) to illuminate a finger. The near infrared light penetrates the finger. Some of that light is scattered, and some is absorbed by hemoglobin in veins. An image sensor, such as a CCD (charge-coupled device) camera, captures an image. The veins appear as dark pixels in that image.
These existing techniques using a 2D projection image are, however, prone to error. Actual vein patterns have a complex three dimensional (3D) structure; whereas a 2D projection image of this 3D structure gives just perspective information viewed from one direction. Thus, vein patterns in a 2D projection image depend sensitively on the rotational and translational position of a finger. In other words, a 2D projection image of the veins may change greatly due to a minor change in the position of a finger. For example, a slight rotation of a finger may cause a 2D projection image of veins to change dramatically, increasing the risk of erroneous vein pattern recognition.